Valley Bottom Areas Research Articles

Sustainable Urbanization in Valley-Bottom Areas in Urban Settings: The Case of the Jaguaré Stream Basin, São Paulo, Brazil

Sustainable Urbanization in Valley-Bottom Areas in Urban Settings: The Case of the Jaguaré Stream Basin, São Paulo, Brazil

From pixels to riverscapes: How remote sensing and geospatial tools can prioritize riverscape restoration at multiple scales

AbstractPrioritizing restoration opportunities effectively across entire riverscape networks (i.e., riverine landscape including floodplain and stream channel networks) can be difficult when relying on in‐channel, reach‐scale monitoring data, or watershed‐level summaries that fail to capture riverscape heterogeneity and the information necessary to implement restoration actions. Leveraging remote sensing and geospatial tools to develop spatially continuous information across nested hierarchical scales may support increased understanding of local riverscape reaches in their broader network context. Using riparian (vegetation) and geomorphic (elevation) indicators to assess status of riverscape health, along with a measure of restoration capacity (valley bottom area), could be adapted to fit specific management goals related to riverscape restoration. Frameworks using remotely sensed vegetation and elevation data to prioritize restoration continuously across riverscapes at restoration‐relevant, reach‐scales may uphold the ecosystem services provided by riverscapes. By incorporating local knowledge and identifying caveats for using these datasets, continuous inferences can be applied at network scales (watershed to regional extent and reach‐scale resolution) to prioritize restoration over a wide variety of ecoregions.This article is categorized under: Water and Life > Conservation, Management, and Awareness Water and Life > Methods Water and Life > Stresses and Pressures on Ecosystems

Basal Melt Patterns around the Deep Ice Core Drilling Site in the Dome A Region from Ice-Penetrating Radar Measurements

Basal melt in the Dome A region will influence the deep-ice-core drilling at Kunlun Station. The melting point (wet bedrock) has a higher reflectivity than the surrounding area, which can be assessed using radar echoes from the bedrock. This paper uses a linear absorption model to determine wet and dry ice–bedrock interfaces around the Kunlun drilling site. In the determination process, an artificial intelligence model was applied to extract the ice–bedrock interface for inferring the ice thickness. Additionally, the various depth-averaged attenuation rates were used to identify the maximal range of basal melting. We mapped the patterns of the wet points on the bottom of the ice sheet and the modeled basal temperature to verify the results of the wet bed conditions. According to these maps of wet bed conditions, the areas with basal melting around the drilling site primarily appear in valley walls with low basal temperatures and are linked with hydraulic potential and bedrock elevation. Identifying the ice–bedrock interface is challenging in the valley bottom area, where the melting points are less than at the valley walls. Additionally, the melting proportions of 11.8% and 3.62% were calculated from two ice-penetrating radar data in this research. The mapped melting points around the site of Kunlun ice core drilling suggest complex ice flow effects and can be used to better interpret archives of old ice for paleoclimate research.

Atlantic Forest birds are more functionally and taxonomically diverse in valley bottoms relative to uplands

The theory behind metacommunity was recently reframed to incorporate the concepts of community ecology. Here we investigate how slight topographic variations might locally create habitat heterogeneity and a system of interchanging bird species (i.e., a metacommunity) in a continuous tropical forest. We studied the distribution of birds in a large and protected Neotropical Forest in southwestern Brazil to understand the influence of valley bottom sites on the taxonomic and functional diversity of the bird communities. As previous studies have shown that specialist species have spatially regular distribution when compared to generalists, in the present study we investigate if topography could influence those local patterns of distribution. We expected (1) to find higher taxonomic and functional diversity in communities of valley bottom areas and (2) lower beta taxonomic and functional diversity of the generalists at the valley bottom, but not of specialists, that should exhibit a somewhat consistent distribution. We gathered information on the composition of local bird communities by deploying eight automatic recording units, four in the valley bottoms and four in the uplands, along 4.3 km trail in the forest interior. Our data showed that bird diversity at the valley bottoms tended to be higher than that at the uplands. Specialist passerine assemblages presented high spatial stability and were regularly distributed throughout the forest. In contrast, generalist passerines have limited trait distribution due to valley bottoms. Because bird communities were distinct from each other, deforestation should have stronger impact in the system if only upland areas are left in the landscape. In this case, species dispersal and coexistence as well as complementary traits have predicted implications for the remaining forest fragments, and management actions should prioritize the conservation of forest fragments that include both bottom valleys and uplands areas.

Coupled hydrological and biogeochemical modelling of nitrogen transport in the karst critical zone

Transport of nitrogen (N) in karst areas is more complex than in non-karst areas due to marked heterogeneity of hydrodynamic behaviour in the karst critical zone. Here, we present a novel, distributed, coupled hydrological-biogeochemical model that can simulate water and nitrogen transport in the critical zone of karst catchments. This new model was calibrated using integrated hydrometric, water stable isotope, and nitrogen-N concentration data at the outflow of Houzhai catchment in Guizhou province of Southwest China. Hydrological dynamics appears to control N load from the study catchment. Combining flow discharge and water stable isotopes significantly constrained model parameterisation and mitigate the equifinality effects of parameters on the simulated results. Karst geomorphology and land use have functional effects on spatiotemporal variations of hydrological processes and nitrogen transport. In the study catchment, agricultural fertilizer was the largest input source of N, accounting for 86% of the total. Plant uptake consumed about 45% of inputs, primarily in the low-lying valley bottom areas and the plain covered by relatively thick soils. Thus, a large amount of N released from soil reservoirs to the epikarst (via fractures or sinkholes) is then exported to the underground channel in the limestone area to the south. This N draining into groundwater could lead to extensive, potentially long-term contamination of the karst system. Therefore, improving the efficiency of fertilization and agricultural management in valleys/depressions is an urgent need to reduce N losses and contamination risk.

Soil temperature survey in a mountain basin

Shallow soil temperature (Tss) was monitored at many clusters of sites in valley bottom areas, bordering mountain slopes, and subalpine upland areas within the Tahoe Basin of the Sierra Nevada, USA. Objectives of this survey were to: (i) accurately log Tss for an entire year across the panoply of ground surface environments that cover the southern Tahoe Basin area, and (ii) identify the primary factors responsible for inter-site variations in seasonal and annual mean Tss. The Tss data for snow-free and annual mean periods exhibit wider inter-site ranges than published observations for other regions, attributable to the great diversity of ground surface environments sampled. Two energy balance based models of ground surface temperature are introduced, each applicable to a wide variety of surface environments and formulated with regional calibration coefficients that can incorporate effects of seasonal snow-cover on annual mean Tss. The models closely fit summer monthly and annual mean Tss data from most sites, and confirm that the large inter-site range of shading (by vegetation and terrain) is responsible for most of the large inter-site range of observed Tss. Additionally, data and model results strongly suggest spatially heterogeneous soil warming rates in response to regional climate warming, and support the value of resolving spatial variations in Tss for groundwater flow tracing techniques.

Characterizing the heterogeneity of karst critical zone and its hydrological function: An integrated approach

AbstractSpatial heterogeneity in the subsurface of karst environments is high, as evidenced by the multiphase porosity of carbonate rocks and complex landform features that result in marked variability of hydrological processes in space and time. This includes complex exchange of various flows (e.g., fast conduit flows and slow fracture flows) in different locations. Here, we integrate various “state‐of‐the‐art” methods to understand the structure and function of this poorly constrained critical zone environment. Geophysical, hydrometric, and tracer tools are used to characterize the hydrological functions of the cockpit karst critical zone in the small catchment of Chenqi, Guizhou Province, China. Geophysical surveys, using electrical resistivity tomography (ERT), inferred the spatial heterogeneity of permeability in the epikarst and underlying aquifer. Water tables in depression wells in valley bottom areas, as well as discharge from springs on steeper hillslopes and at the catchment outlet, showed different hydrodynamic responses to storm event rainwater recharge and hillslope flows. Tracer studies using water temperatures and stable water isotopes (δD and δ18O) could be used alongside insights into aquifer permeability from ERT surveys to explain site‐ and depth‐dependent variability in the groundwater response in terms of the degree to which “new” water from storm rainfall recharges and mixes with “old” pre‐event water in karst aquifers. This integrated approach reveals spatial structure in the karst critical zone and provides a conceptual framework of hydrological functions across spatial and temporal scales.

Geomorphic consequences of rapid deglaciation at Pasterze Glacier, Hohe Tauern Range, Austria, between 2010 and 2013 based on repeated terrestrial laser scanning data

Since the end of the Little Ice Age around 1850 CE glaciers in the Alps have been receding dramatically. This study aimed to quantify and characterize the geomorphic and landform changes of a 0.9 km2 large proglacial area at the largest glacier in Austria (Pasterze Glacier, Austria, N 47°04′, E 12°44′). Point clouds from multiple terrestrial laserscanning (TLS) and different image data were used to quantify surface elevation changes and distinguish different types of erosional and depositional landforms during the period 2010–2013. Results indicate that the study area is characterized by a total volume loss of 1,309,000 m3. Excluding the area which was deglaciated, the volume loss equals 275,000 m3 in the period 2010–13. The decrease is related to sediment transfer out of study area and due to sediment-buried glacier ice which is slowly melting. The landform classification reveals that drift mantled slopes are most frequent (20.9% of the study area in 2013) next to ice contact terrace landforms (19.7%). In terms of vertical surface elevation changes, our results suggest distinguishing between 3 distinct domains within the study area: (i) a flat valley bottom area consisting of water/sandur areas and ice-cored landforms dominated by widespread subsurface ice melting and lateral fluvial (and thermal) erosion; (ii) a gently-sloping footslope area consisting of ice-contact sediments, former ice marginal channels and deep incised gullies with corresponding debris cones dominated by linear erosion and corresponding deposition; and (iii) a steep lateral slope area mainly built up of consolidated drift material with incised gullies dominated by linear erosion. Our results not only confirm the previously revealed high geomorphic activity for proglacial areas of alpine glaciers in terms of surface elevation variations, they also highlight that landforms might change substantially from one year to the next not only because of erosional/depositional processes, but also because of the melting of buried dead-ice bodies.

Domination of hillslope denudation by tree uprooting in an old-growth forest

Razula forest preserve in the Carpathian Mountains of the Czech Republic is an unmanaged forest that has not been logged or otherwise anthropically disturbed for at least 83years, preceded by only infrequent selective logging. We examined this 25ha area to determine the dominant geomorphological processes on the hillslope. Tree uprooting displaces about 2.9m3 of soil and regolith per year, representing about 1.5uprootedtreesha−1yr−1, based on forest inventory records dating back to 1972, and contemporary measurements of displaced soil and pit-mound topography resulting from uprooting. Pits and mounds occupy >14% of the ground surface. Despite typical slope gradients of 0.05mm−1, and up to 0.41, little evidence of mass wasting (e.g., slump or flow scars or deposits, colluvial deposits) was noted in the field, except in association with pit-mound pairs. Small avalanche and ravel features are common on the upslope side of uproot pits. Surface runoff features were rare and poorly connected, but do include stemwash erosion associated with stemflow. No rills or channels were found above the valley bottom area, and only small, localized areas of erosion and forest litter debris indicating overland flow. Where these features occurred, they either disappeared a short distance downslope (indicating infiltration), or indicate flow into tree throw pits. Surface erosion is also inhibited by surface armoring of coarse rock fragments associated with uprooting, as well as by the nearly complete vegetation and litter cover. These results show that the combination of direct and indirect impacts of tree uprooting can dominate slope processes in old-growth, unmanaged forests. The greater observed expression of different hillslope processes in adjacent managed forests (where tree uprooting dynamics are blocked by management activities) suggests that human interventions can change the slope process regime in forest ecosystems.

Investigation of the Curve Number Method For Surface Runoff Estimation In Tropical Regions

AbstractThis study tests the applicability of the curve number (CN) method within the Soil and Water Assessment Tool (SWAT) to estimate surface runoff at the watershed scale in tropical regions. To do this, surface runoff simulated using the CN method was compared with observed runoff in numerous rainfall‐runoff events in three small tropical watersheds located in the Upper Blue Nile basin, Ethiopia. The CN method generally performed well in simulating surface runoff in the studied watersheds (Nash‐Sutcliff efficiency [NSE] > 0.7; percent bias [PBIAS] < 32%). Moreover, there was no difference in the performance of the CN method in simulating surface runoff under low and high antecedent rainfall (PBIAS for both antecedent conditions: ~30%; modified NSE: ~0.4). It was also found that the method accurately estimated surface runoff at high rainfall intensity (e.g., PBIAS < 15%); however, at low rainfall intensity, the CN method repeatedly underestimated surface runoff (e.g., PBIAS > 60%). This was possibly due to low infiltrability and valley bottom saturated areas typical of many tropical soils, indicating that there is scope for further improvements in the parameterization/representation of tropical soils in the CN method for runoff estimation, to capture low rainfall‐intensity events. In this study the retention parameter was linked to the soil moisture content, which seems to be an appropriate approach to account for antecedent wetness conditions in the tropics.

Using geophysical surveys to test tracer‐based storage estimates in headwater catchments

AbstractHydrogeophysical surveys were carried out in a 3.2 km2 Scottish catchment where previous isotope studies inferred significant groundwater storage that makes important contributions to streamflow. We used electrical resistivity tomography (ERT) to characterize the architecture of glacial drifts and make an approximation of catchment‐scale storage. Four ERT lines (360–535 m in length) revealed extensive 5–10 m deep drift cover on steeper slopes, which extends up to 20–40 m in valley bottom areas. Assuming low clay fractions, we interpret variable resistivity as correlating with variations in porosity and water content. Using Archie's Law as a first approximation, we compute likely bounds for storage along the ERT transects. Areas of highest groundwater storage occur in valley bottom peat soils (up to 4 m deep) and underlying drift where up to 10 000 mm of precipitation equivalent may be stored. This is consistent with groundwater levels which indicate saturation to within 0.2 m of the surface. However, significant slow groundwater flow paths occur in the shallower drifts on steeper hillslopes, where point storage varies between ~1000 mm–5000 mm. These fluxes maintain saturated conditions in the valley bottom and are recharged from drift‐free areas on the catchment interfluves. The surveys indicate that catchment scale storage is >2000 mm which is consistent with tracer‐based estimates. Copyright © 2016 John Wiley & Sons, Ltd.

Research on the surface movement in a mountain mining area: a case study of Sujiagou Mountain, China

Landslides caused by underground mining are very common in mountain mining areas, and thus threaten human lives and assets. Under the superposed influence of underground mining and landslides, surface movement in mountain areas is different from that in flat areas. Further understanding of the law of surface movement in mountain mining areas can protect the locals and their assets. In this study, an improved survey technique called spherical fitting real-time kinematic was employed to monitor surface movement regularly, and similar material simulation was used as a supplement to reveal the process of strata failure. Results showed that the ground would uplift during underground mining in the valley bottom areas, an action that caused the subsidence velocity curve to appear as a skewed distribution instead of a Gaussian distribution. To improve the prediction accuracy, the prediction model of surface subsidence in mountain mining areas was updated. The mountain surface subsidence prediction system was developed using Visual Basic. Finally, the mechanism of mining landslide was studied. This work is of general interest to the professional public and it will contribute to a more objective knowledge of understanding the surface movement in mountain mining areas.

Baseflow dynamics: Multi-tracer surveys to assess variable groundwater contributions to montane streams under low flows

Summary We monitored changing groundwater-surface water interactions during a drought with a 10 year return period in a 3.2 km 2 catchment in the Scottish Highlands. The montane catchment is underlain by granite and metasediments and has extensive cover of diverse drift deposits (70%), which are up to 40 m deep. Flat valley bottom areas fringing the stream channel are characterised by deep peat soil (0.5–4 m deep) which covers about 20% of the catchment and receive drainage from upslope areas. The drought resulted in small declines in soil moisture and groundwater levels in the valley bottom wetlands, but marked, rapid declines on steeper upland slopes. These coincided with gradual decreases in discharge; however, the chemical and isotopic composition of reduced stream flows showed both temporal and spatial variation. Synoptic hydrogeochemical surveys were carried out on four occasions as flows declined. Each survey repeated sampling of 26 sites along the 3 km long stream network. Samples were analysed for major anions, cations and water isotopes. Initial surveys just after the last winter rain showed relatively homogenous stream chemistry, consistent with dominant near-surface drainage from acidic riparian peat soils. Stream chemistry became increasingly enriched with weathering-derived solutes (e.g. alkalinity, Ca 2+ , Mg 2+ , etc.) as flows declined and groundwater dominance of flow increased. However, these changes showed marked spatial variability implying geochemical differences in the bedrock geology and the distribution of storage in drift deposits. Temporal dynamics inferred heterogeneous montane groundwater bodies contributed to flows differentially during the recession. Isotope data indicated that in places the stream was also influenced by evaporative losses from the surface of the peat soils. The largest sources of groundwater appear to be located in the drift in the lower catchment where the most marked increase in weathering-derived ions occurred, and depleted, non-fractionated isotope signatures implied deeper inflows.

Upland sediment supply and its relation to watershed sediment delivery in the contemporary mid-Atlantic Piedmont (U.S.A.)

We use sediment accumulation in ponds and reservoirs to examine upland sediment sources and sinks in the Piedmont physiographic region of Maryland, USA. In zero-order and first-order watersheds, sediment yield is greatest from suburban land cover, followed by agriculture and forest. The idea that sediment yield is small from mature suburban development appears to not be correct. First-order channel enlargement is an important sediment source, causing sediment yield to increase from zero-order to first-order watersheds. Nonchannel sources provide one-third to two-thirds of the upland sediment load.Long-term sediment accumulation in a reservoir at fifth-order indicates that cumulative sediment load from upland areas is reduced by one-quarter by net valley bottom sedimentation. If upland supply exceeds the load delivered from a watershed, sediment must accumulate along valley bottoms. In our study watershed, net sedimentation rate (sedimentation less erosion) averaged over valley bottom area is 2.6mm/y, a value that is similar to independent direct measurements of sedimentation and erosion in a nearby watershed. Evaluation of the relative contributions to sediment mass balance of upland supply, valley bottom sedimentation and erosion, and watershed delivery indicates that, if valley-bottom rates of sedimentation exceed erosion as indicated by recent studies, then the proportion of watershed sediment delivery derived from stream banks is necessarily small.Although sediment yield estimated from stream gage records is similar in magnitude to that from ponds for watersheds smaller than 20km2, sediment yield from reservoir sedimentation is a factor of five larger than that estimated from gage records for watersheds larger than 140km2. This observation confirms that the different methods provide very different estimates of sediment yield. This possibility is reinforced by a sediment yield of 14Mg/km2/y from a gage immediately above a reservoir with a yield of 142Mg/km2/y based on reservoir accumulation.

Modelling landscape controls on dissolved organic carbon sources and fluxes to streams

Catchment dissolved organic carbon (DOC) fluxes are governed by complex interactions, which control biogeochemical processes generating DOC and hydrological connectivity, facilitating transport through the landscape to streams. This paper presents the development of a coupled hydrological-biogeochemical model for a northern watershed with organic-rich soils, to simulate daily DOC concentrations. The parsimonious model design allows the relative importance of DOC fluxes from the major landscape units (e.g. hillslopes, groundwater and riparian saturation area) to be determined. The dynamic extent of the saturated riparian zone, which at maximum wetness comprised 40 % of the drainage area, contributed 84 % of DOC to the stream, of which 16 % was derived from the hillslope soils. This shows the disproportional riparian influence on stream water chemistry and the importance of the non-linearity in hydrological connectivity. The temporal connectivity of each of the landscape units was dependent on antecedent moisture conditions, with highly transient connections between the hillslope and valley bottom saturated area, which were entirely disconnected during the driest periods. The groundwater contribution remained constant, but its relative importance increased during the driest periods. The study emphasises the importance of conceptualising hydrological connectivity and its relation to hydroclimatic factors, as well soil biogeochemical processes, when modelling stream water DOC.

Implications of hydrologic connectivity between hillslopes and riparian zones on streamflow composition

Hydrological responses in mountainous headwater catchments are often highly non-linear with a distinct threshold-related behavior, which is associated to steep hillslopes, shallow soils and strong climatic variability. A holistic understanding of the dominant physical processes that control streamflow generation and non-linearity is required in order to assess potential negative effects of agricultural land use and water management in those areas. Therefore, streamflow generation in a small pre-Alpine headwater catchment (Upper Rietholzbach (URHB), ~1km2) was analyzed over a 2-year period by means of rainfall-response analysis and water quality data under explicit consideration of the joint behaviors of climate forcing and shallow groundwater dynamics. The runoff coefficients indicate that only a small fraction of the total catchment area (1–26%) generates streamflow during rainfall events. Hereby, the valley bottom areas (riparian zones) were the most important event-water source whereas only the lower parts of the hillslopes became hydrologically connected to the river network with higher antecedent moisture conditions. However, a distinct threshold-like behavior could not be observed, suggesting a more continuous shift from a riparian-zone to a more hillslope-dominated streamflow hydrograph. Regular manure application on the hillslopes in combinations with lateral hillslope groundwater flux and long groundwater residence times in the riparian zones resulted in a higher mineralization (e.g., total phosphorous) and significant denitrification in the valley bottom area. Despite the important role of the riparian zones for event-flow generation in the URHB, their nutrient buffer capacity is expected to be small due to the low permeability of the local subsurface material. The findings of this integrated analysis are summarized in a conceptual framework describing the hydrological functioning of hillslopes and riparian zones in the URHB.

Post-fire tree recruitment of a boreal larch forest in Northeast China

Boreal larch forests in eastern Siberia contain about half of the carbon accumulated in Eurasian forest communities, and fire is an important disturbance in this area, contributing to changes in forest composition and breaking the original succession trajectory. Assessing burn severity and environmental controls on post-fire larch recruitment is critical for understanding long-term effects of fire disturbance on forest succession in this region. A mega-fire that burned 8700ha in the year 2000 in the Great Xing’ an Mountains provided an opportunity to study the effects of mixed-severity fire disturbance in larch forests. We sampled tree recruitment in 83 burned sites to address the question of how burn severity and site environment interact to influence the species composition and density of post-fire tree recruitment, and hence the successional trajectory of forest. We explored the hypothesis that the larch forest was more likely to replace itself rapidly (“self-replacement succession”) in areas of low-severity burn, but was more likely to be replaced by an early-seral community of broadleaf trees (“relay succession”) in areas of high-severity burn. Our analysis showed that post-fire conifer and broadleaf recruit densities were both negatively related to burn severity and understory cover. Environmental conditions (e.g. elevation, slope, aspect) had weaker influences than burn severity on post-fire tree densities, but played a stronger role in determining the relative proportion of conifer recruits. Broadleaf trees recruited abundantly in low-severity burns in upland areas, even though they were absent from most of the pre-fire sites. In contrast, coniferous trees recruited more abundantly in low-severity burns in valley bottom areas. The comparison of pre- and post-fire tree composition in the burned patches indicated that self-replacement succession was likely to occur in valley bottom areas that burned with low severity. Burned upland areas are more likely to experience an alternative, broadleaf-dominated trajectory of relay succession. The increase in the severity and frequency of fires due to climate warming may prompt shifts from a larch dominated forest to an increasingly birch dominated landscape, substantially altering landscape dynamics and ecosystem services.

Natural and logging disturbances in the temperate rain forests of the Central Coast, British Columbia

Natural disturbances frame the spatial and temporal processes of ecosystems and are the foundation for ecosystem-based management. In the coastal temperate rain forests of British Columbia, landscape patterns of natural disturbances and their contrasts with logging are not well documented. Stand-replacing disturbances over the past 140 years were investigated for the Central Coast (1.5 million ha) at regional and local scales using a combination of aerial photograph interpretation and forest management GIS databases. At the regional scale, stand-replacing natural disturbances affected 3.1% of the forested area. The extent of natural disturbances was not strongly affected by the scale of analysis. In contrast, spatial pattern and scale were essential for discerning the full impact of logging. At the regional scale, logging affected 5.4% of the forested area. Within watersheds, however, logging occurred primarily in valley bottoms (81% ± 4%) with 59% ± 10% of valley bottom areas logged, 10 times the area of natural disturbances. Watershed size strongly affected riparian zones, with active floodplains comprising 53% ± 5% of valley bottom area in large (>20 000 ha) watersheds. In physiographically diverse landscapes, geomorphic features (such as watersheds, valley bottoms, and fluvial landforms) are crucial for determining disturbance processes and effects of logging at ecologically relevant scales.

Occurrence of PAH in the seasonal snowpack of the Eastern Italian Alps

PAH concentrations have been determined in 47 seasonal snowpack samples collected in the Valbelluna valley and in the Bellunesi Dolomites National Park, in the Italian North-Eastern Alps, during the winter of 2005. The ΣPAH concentration in high-altitude alpine sites (above 1700 m) was 32 ± 20 ng/kg while in valley bottom urban areas it was 165 ± 54 ng/kg with maximum values of 290 ng/kg. The GIS mapping technique was employed to produce a PAH spatial distribution. The urbanized Valbelluna valley, and in particular the SW part, had the highest accumulation of all PAH, with values an order of magnitude more than those in rural and alpine areas. This behaviour is consistent with urban air quality data, and is due to geo-morphological and meteorological factors such as the deeper shape of the valley at the position of the town of Feltre and the low altitude of the boundary layer during the winter season.

Evaluating the sensitivity of DRASTIC using different data sources, interpretations and mapping approaches

When used in a comprehensive risk assessment framework, aquifer vulnerability maps are a tool to identify the relative susceptibility of the groundwater from sources of contamination at the land surface. The DRASTIC method was designed for use over large areas with a wide variety of geological and hydrogeologic settings as a screening tool in groundwater protection and management. In this study, a series of vulnerability maps were made for the Greater Oliver area, in south central Okanagan, British Columbia, Canada, to test the sensitivity of the methodology to changes in input data type, interpretation, and mapping approaches. The study also illustrates how DRASTIC can be modified for use in areas of limited geological variability, where it may be important for smaller-scale changes in vulnerability to be recognized. Maps were produced using the original DRASTIC rating tables, a set of expanded tables using the original properties but modified ranges to accommodate the variability of data in the valley bottom region, and alternate tables, with modified properties and ranges. Differences in vulnerability rating for the maps using selected combinations and data interpretations are compared to the map using original DRASTIC rating tables using visual and statistical methods. One map was generated using expert hydrological knowledge. The modified tables allowed a greater amount of variability to be expressed in the valley bottom area compared to using the original tables and methods, and could provide a reasonable approach for assessing local scale variability for source water protection planning.